To fulfill the promise of regenerative medicine in the cardiac myogenesis field, it will be necessary to effectively manipulate expansion, differentiation, and maintenance of cardiac progenitor cells. This will be required regardless of whether translational researchers attempt to augment endogenous regenerative capacity via recruitment of progenitor cells in vivo, or whether progenitors are generated and expanded ex vivo for subsequent delivery or for the generation of tissue engineered bioprostheses. The importance of a detailed understanding of the signaling pathways important for progenitor expansion and proper differentiation is emphasized by analogous advances in the hematopoietic field, where the clinical use of GM-CSF, G-CSF and related growth factors, which regulate stem cell expansion has provided dramatic clinical impact. In the cardiovascular field, the ability to specifically regulate progenitor cell survival, expansion and differentiation is generally lacking. Moreover, a usable source of progenitors for ex vivo expansion remains elusive. To overcome this limitation, many studies have focused on the generation and characterization of cardiac progenitors from embryonic stem cells as well as induced pluripotential stem cells derived from non-cardiac fibroblasts for eventual use in tissue engineering therapies. These studies have shown that cardiac myocytes can be generated from such cell types but have also revealed that the resulting myocytes do not exhibit all of the necessary characteristics of adult cardiac myocytes. The ability to expand and controllably differentiate cardiac myocytes from ES or IPS cells is therefore limited in its uses, in part due to the lack of understanding of how cardiac progenitors expand and differentiate in vivo. The underlying thesis of the Penn/UW Consortium application is that further elucidation of the signals that mediate cardiac and hematopoietic progenitor development in the embryo provides a logical approach for the identification of factors useful for expansion and differentiation of progenitor cells ex vivo. Hence, our collaborative projects combine the analysis of two of the most vital stem cell signaling pathways, Wnt and Notch, during development and in cardiac and blood progenitors derived from pluripotential stem cells including ES and iPS cells. Nevertheless, this analysis remains undeveloped and the interactions of Wnt and Notch in the developing heart remain unexplored, although these pathways are known to interact in many other stem cell populations. These studies will interface with those described in the collaborative linked application on the role of Wnt and Notch in expansion and proper differentiation of hematopoietic stem cells (HSCs). The Aims of the UPenn cardiac portion will focus on 1) how Wnt and Notch promote cardiac progenitor expansion and differentiation in development and in ES/iPS cells and 2) defining the similarities and differences between Wnt and Notch manipulated cardiac myocytes and mature adult myocytes. Thus, the Penn/UW Progenitor Consortium proposes to characterize the ability of Wnt and Notch signaling to expand progenitors in vivo as well as ex vivo.